Laces can be tied tightly or loosely, depending upon the preference of the wearer. Even a custom-made shoe benefits from the adjustability provided by laces, since both the dimensions of a foot and the tightness/looseness preference can change in the course of the day. To accommodate a nearly unlimited range of foot shapes and sizes, however, a sufficient amount or a limited amount of slack must be provided.
Shoe laces present a simple engineering concept that does not always perform as planned. A shoe lace should be designed to slide easily through the eyelets or holes provided in the shoe or sneaker. This is necessary so that a proper setting of size and tension is achieved. However, once the lace is tied, it should stay tied. On close observation, it will be noted that these two requirements are diametrically opposed. Many laces, while easy to adjust, fail to stay tied, once knotted. To illustrate this problem, consider a newspaper account of a Marathon runner named John Kagwe: "Just one problem with the Nike Air Vengeance: the laces kept untying. `And I had triple knots,` said Kagwe, of Kenya. Stopping twice to tie his shoes, and running the last four miles with the right lace flapping, Kagwe won the marathon in two hours, eight minutes, and twelve seconds through 26.2 miles in the rain . . . "
Several inventors have addressed the problem of keeping laces adequately tied. In U.S. Pat. No. 5,272,796, issued to Nichols on Dec. 28, 1993 for SLIP RESISTANT SHOE LACE AND METHOD FOR MANUFACTURING SAME, a slip resistant shoe lace is illustrated. Strands of higher frictional coefficient are woven internally of the outer perimeter of the lace, in order to provide a frictionally enhanced lace that will not slip its knot.
In U.S. Pat. No. 4,780,936, issued to Brecher on Nov. 1, 1988 for STAY-TIED SHOE LACES, a shoe and lace combination is shown that impedes the loosening of a tied lace. The tongue of a shoe is provided with a flexible band member that folds over the lace after it has been knotted. The band secures the knot from unraveling. The flexible band is itself held in its fold-over position by means of a Velcro patch disposed thereupon, that mates with a corresponding patch on a distal end thereof.
In U.S. Pat. No. 5,673,546, issued to Abraham et al. on Oct. 7, 1997 for NON-SLIP SHOELACES, a slip resistant shoe lace is illustrated. The lace features a plurality of special slip resistant yarns that contains slubs. The slubs, when woven into a lace, provide a length of material that has protuberances disposed along the length of the lace. These protuberances are meant to provide frictional "bumps" at periodic intervals, which bumps will prevent a tied lace from unravelling its knot.
None of these lace systems, however, has addressed the concurrent problem of assuring that the laces easily slide through the eyelets or holes provided for them. Indeed, these laces will resist becoming untied once knotted, but they are now more likely to resist being threaded through the eyelets of a shoe or sneaker. Adding frictional means within the yarn solves the problem of unravelling, but exacerbates the problem of threading the lace through the eyelets of the shoe. As aforementioned, the two objectives compete with each other, and require opposite design criteria.
In present day laces, the yarn presents a compromise between the competing objectives. One is forced to choose between non-slippage and ease of threading.
The present invention is a shoe lace that is easily threaded, looped, and adjusted through the eyelets of a shoe, while at the same time is capable of forming a non-slip knot, when tied.
One embodiment of the inventive device is a flat shoe lace comprising an upper and lower surface made of different materials. The novel lace configuration performs a function similar to that of hook-on-one-side, pile-on-the-other-side fasteners. Unlike Velcro.RTM., however, the surfaces are not designed for adhesion, but for high static friction between the upper and lower surfaces of the flat lace. When tying the flat shoe lace, both surfaces inevitably come in contact with each other. In this way, the laces resist inadvertent untying. Both the upper and lower surfaces have a low coefficient of both static and sliding friction with respect to the eyelets or holes. This enables the lace to be threaded through with minimal effort.
Alternative embodiments for obtaining high lace-to-lace friction and negligible lace-to-eyelet friction are described in detail hereinbelow.
While the various embodiments describe flat or rectangular shaped laces, the novel design approach would also be applicable to a lace with a round or oval cross-section.